Fenton's reagent, first found by English chemist Fenton in 1894, is a kind of oxidation system composed of hydrogen peroxide and catalyst Fe2+, in which the Fe2+ ion is mainly used as a homogeneous catalyst, while H2O2 plays the role of oxidant. Fenton's reagent is more widely used in industrial wastewater treatment, especially wastewater which is difficult to deal with or of biological toxicity (such as cyanide contained wastewater), due to its advantages of rapid response, mild reaction condition and no secondary pollution etc. Generally, in acidic conditions, such as pH=3.5, Fenton's reagent has strong oxidative property. Organic compounds, such as carboxylic acids, alcohols, esters etc., can be directly oxidized into carbon dioxide and water (Journal of hazardous materials, 2003, 98, 33-50; Industrial water treatment, 2014, 3, 22-25). Under the alkaline conditions, Fenton's reagent was also applied in cyanide contained wastewater treatment (Environmental Toxicology and Chemistry, 1994, 13, 1719-1726; Water Treatment Technology, 2012, 38, 114-117). However, applications of Fenton's reagent in other aspects are rare.
Metal cyanides are compounds that metal ions and cyano are connected directly, which are of hypertoxicity. Cyanide ions may free out after metal cyanides get into the human body, and then combine with ferric iron of cytochrome oxidase, preventing the reduction of ferric. As a result, the normal cell respiration may be disturbed, causing tissue hypoxia and body suffocation. On the other hand, metal cyanides have a wide range of uses. For example, the use of cyanide in industrial mining of gold, silver and organic synthesis (using metal cyanide to synthesis of nitrile). Meanwhile, metal cyanides also play a vital role in electroplating, dye, and paint industrial process.
For hundreds of years, there is only one way to synthesis noble metal cyanides and transition metal cyanides, namely the traditional synthesis method (J. Chem Soc. 1943, 79; J. am. Chem Soc. 2012, 134, 16387-16400). This method uses NaCN, KCN or HCN as the source and formation of cyano, which react with metal or metal ion directly. In the case of cyanide gold synthesis, the traditional synthesis method is mainly the MacArthur-Forrest process, which is divided into the following two steps:4Au+8NaCN+O22H2O=4Na[Au(CN)2]+4NaOHKAu(CN)2+HCl═AuCN+HCN+KCl
The reaction is related to the free cyanide ion, which is of fatal threat to the environment and human health. Besides, the cyanide ion is easy to combine with the ferric ion to form the iron cyanide, making it difficult to generate other metal cyanide in the presence of iron ions.
In 2012, the inventors established a UV method for metal cyanide preparation (CN 102274740 A). The UV method overcomes the problem of cyanide ion in the traditional technology, but this method uses relatively expensive UV light, easy to produce light pollution, and it is difficult to achieve industrialization. At the same time, the inventors found that it is difficult to control the cyanation degree during gold cyanide preparation through UV method, and the product quality is unstable, and it is difficult to synthesize multi metal cyanide through this UV method. Therefore, the development of a cheap, simple, efficient, green and controllable method for metal cyanides preparation may be of great significance.